Abstract: Objective:To study the effect and mechanism of bone marrow mesenchymal stem cells (BMMSCs) exosomes on promoting osteogenic differentiation of periodontal ligament stem cells (PDLSCs) via regulating signal transducer and activator of transcription 3 (STAT3) pathway. Methods:BMMSCs and PDLSCs were primarily cultured, and the exosomes were isolated from the third generation BMMSCs. The third generation PDLSCs were taken for osteogenic induction and grouped, the exosomes group was treated with 15 μg/mL exosomes and phosphate buffer (PBS), the PBS group was treated with equal volume of PBS, and the antagonist group was treated with 15 μg/mL exosomes and 50 μmol/L STAT3 antagonist AG490 in dimethyl sulfoxide (DMSO) as solvent, (exosome＋DMSO) group was treated with 15 μg/mL exosomes and equal volume of DMSO, DMSO group was treated with equal volume of DMSO and phosphate buffer. The level of A540 was detected. The expression levels of alkaline phosphatase (ALP), osteocalcin (OCN), type I collagen (Col-Ⅰ), phosphorylated janus kinase 2 (p-JAK2) and phosphorylated-STAT3 (p-STAT3) were detected 7 days after induction. Alizarin red staining was performed 21 days after induction, and optical density (OD) was detected. Results:The OD level and the expression levels of ALP, OCN, Col-Ⅰ, p-JAK2 and p-STAT3 of PDLSCs in exosome group were higher than those in PBS group (P<0.05). The results of antagonist group were lower than those in (exosomes＋DMSO) group (P<0.05). Conclusions:BMMSCs exosomes promote the osteogenic differentiation of PDLSCs via activating JAK2/STAT3 pathway.